1. Field of the Invention
The invention relates to gear reduction units and is particularly applicable to mixing apparatus and methods. A motor driven gear reduction unit has at least two parallel shafts coupled respectively to a driving pinion gear and a driven gear meshing with the pinion gear. A first such shaft and its gear (the input pinion) are carried on a self contained mounting or cartridge that pivots the first shaft around a pivot axis parallel to and spaced from the axis of the other shaft. Pivoting the mounting changes the distance between the rotational axes of the two shafts and allows either or both of the driving and driven gears to be replaced with gear(s) of a different diameter.
In a mixer drive embodiment, different diameter pinions can be selected and installed to mesh with a given diameter low speed driven gear for choosing the reduction ratio of the drive. Pivoting the cartridge eccentrically carrying one or more pinions moves the meshing pinion clear of the low speed gear such that the cartridge can be lifted out of the drive. In a multiple reduction arrangement, pivoting also can move an intermediate reduction pinion clear of the low speed gear, enabling the cartridge to be lifted clear. Among other benefits, the drive conveniently allows different diameter gears to be installed on the respective shafts for changing gear reduction ratios and/or substitution of cartridges with single and plural reduction stages, without substantially reconfiguring the mixing apparatus to do so.
2. Prior Art
There are various situations in which it may be desirable to configure a geared drive to have a particular reduction ratio. A basic gear reducer comprises two parallel spaced shafts that are rotationally mounted in suitable bores, bearings or similar fittings in a housing. Fixed to the shafts are meshing gears of which one is a driving gear and one is a driven gear. If a particular reduction ratio (or perhaps increasing ratio) is needed to obtain predetermined torque and speed characteristics, the diameters of the gears are selected accordingly. Whereas the gears must mesh and the spacing of the parallel shafts typically is fixed by the fittings in the housing, enlarging the diameter of one gear is accompanied by decreasing the diameter of the other gear, and vice versa.
A mixer for industrial and commercial applications involving the mixing and agitation of liquids, liquid suspensions and other materials, typically comprises an impeller on a vertical shaft extending into a container for mixing the contents of the container by rotation of the impeller. A motor is coupled to the shaft, generally through reduction gears that reduce rotational speed and increase mechanical advantage between the motor and the impeller for developing sufficient torque. This can involve single pairs of gears or multiple pairs. Relatively smaller diameter gears are provided on the motor side of the gear train and relatively larger diameter gears on the impeller shaft side.
An example of a drive apparatus for such a mixer having a housing forming a lubricant well is disclosed in U.S. Pat. No. 4,721,003--Hutchings et al., the disclosure of which is hereby incorporated. The drive apparatus has a housing with a base having an upwardly and inwardly extending tubular part and surrounding sidewalls, forming a lubricant receptacle between the tubular part and the sidewalls. A vertical impeller shaft extends upwardly into the housing. A rotatable hub surrounding the tubular part is affixed to the impeller shaft and carries a large low speed gear at an elevation below the upper edges of the sidewalls and the tubular part, namely in the lubricant receptacle. A drive shaft, for example coupled to an electric motor, is spaced from and parallel to the impeller shaft. A relatively smaller high speed pinion gear on the drive shaft meshes with the larger low speed gear on the hub. The hub bridges over the tubular part and the hole therein, coupling with the impeller shaft via a split ring clamping structure. The impeller shaft extends through the hole and is located by its coupling with the hub to leave an annular gap between the impeller shaft and the tubular part. The gap defines a radial running clearance for the impeller shaft and receives a seal assembly.
The body of the motor protrudes upwardly from a mounting on a cover of the housing, and is flexibly coupled to the drive shaft carrying the pinion. The drive shaft forms an extension of the shaft of the motor. The drive shaft is journalled by bearings disposed in inwardly extending flanges of the base of the housing. This structure fixes the positions of the driving and driven shafts, and more particularly makes the spacing of the axes of the shafts invariable. It is possible to employ additional reduction gearing with one or more intermediate shafts journalled in the housing and being mechanically coupled between the motor and the driven shaft. Such an intermediate shaft can be provided with a larger gear coupled to a motor shaft pinion and a smaller pinion coupled to the low speed gear. In that case, the relative positions of each of the motor shaft, the intermediate shaft and the driven impeller shaft are fixed with respect to the housing by bushings or bearings rigidly mounted in the walls or flanges of the housing.
Mixers may be applied to mix or agitate compositions over a wide range of viscosities, densities and attributes, and may need to do more or less shaft work on the compositions depending on the particular process involved. Different processes and different compositions call for different impeller rotation speeds and different torque requirements. In a stable process, a mixer can be configured to provide the optimal speed and torque, but for process variations and job changes, different requirements may necessitate variable speed drives and different gear ratios.
In a mixer such as that of U.S. Pat. No. 4,721,003--Hutchings et al., or a similar device in which the drive shaft pinion and/or motor are eccentric to the impeller shaft, it is necessary to remove and replace both gears in each intermeshing pair to change the gear reduction ratio. This is because the axes of the drive shaft and the impeller shaft are fixed. To reduce the reduction ratio, for example, the larger or low-speed gear is replaced with a gear having a smaller outside diameter, and the smaller or high-speed gear is replaced with a gear having a correspondingly larger outside diameter so that the two new gears mesh. In a device such as the Hutchings mixer, this involves replacing both the drive shaft pinion and the low speed gear, and substantially disassembling and reassembling the drive mechanism. In a mixer having an additional reduction gear pair, four gears might have to be replaced, etc. Even if the object is to supply a range of mixers with different speed/torque characteristics (rather than to reconfigure a mixer), it would be advantageous if the gear reduction ratio could be changed more conveniently and without requiring an undue inventory of parts.
A modular mixer drive system is disclosed in U.S. Pat. No. 5,149,194--Engels et al. The motor, transmission, bearing housing and impeller shaft components are all modularly replaceable to reconfigure a mixing apparatus for particular mixing applications. The components may be assembled to provide direct drive from the motor to the impeller shaft (without reduction gears), or through a gear transmission having a chosen reduction ratio. The Engels arrangement uses a coaxial motor and impeller shaft coupled (if desired) by one or more planetary gear trains wherein the diameters of the gears determine the reduction ratio. Engels thereby allows the reduction ratio to be changed by swapping gear reduction modules. Only the bearing housing is common to all of the variations, which can receive any of a plurality of gear sets. Nevertheless, substantial disassembly and reassembly steps are required to make a gear reduction change, and an inventory of complementary large and small planetary gears is needed to meet a range of speed/torque requirements.
According to an aspect of the present invention, the reduction ratio of a mixer drive unit can be altered by changing the diameter of one of a pair of meshing gears, mounted in an eccentric cartridge to provide variable shaft center distances. The cartridge can be rotated for adjusting the distance between the axes of the shafts carrying the gears. According to a further aspect, the motor shaft carrying a pinion gear is eccentrically mounted in a unitary cartridge that is rotatable in the housing carrying the impeller shaft. The pivotal coupling of the cartridge to the housing is on an axis spaced from and parallel to both the driving pinion shaft and the driven shaft (e.g., the impeller shaft or relatively slower speed gear). By rotating the cartridge, the eccentric pinion rotation axis is moved toward or away from the driven gear. This has been found to provide a quick and convenient way to configure or change reduction ratios that does not involve substantial disassembly of the mixer drive unit in order to configure the mixer for different requirements of speed and/or torque, and does not require changing the diameters of both meshing gears.
According to a further inventive aspect, the pivotal cartridge, which can be provided with pinion gears of different diameters, is disposed within the side walls of the mixer housing in the lubricant reservoir. However, without disassembling the entire housing, the cartridge can be pivoted outwardly to disengage the pinion from the driven shaft gear. The unitary cartridge then can be lifted free. Likewise, the cartridge can be provided with a different diameter pinion, inserted into the housing and pivoted to engage the pinion with the driven shaft gear.
In a multiple stage gear reduction arrangement, the motor shaft pinion can drive the larger gear on an intermediate shaft having a smaller pinion driving the large low speed gear. In such an arrangement, the larger gear on the intermediate shaft extends below the large low speed gear that meshes with the smaller pinion. The pivotable cartridge of the invention readily pivots outwardly to clear the larger gear on the intermediate shaft from the large low speed gear, making the invention particularly apt for multiple reduction gears.